Serial ATA (Advanced Technology Attachment) is an evolutionary replacement for the Parallel ATA physical storage interface. Serial ATA (SATA) is a computer bus primarily designed for transfer of data between a computer processor and hard disk and has at least three advantages over Parallel ATA, namely speed, cable management, and Serial ATA's ability of being hot swappable. A Serial ATA host controller may use a combination of specialized hardware and a general purpose Input Output Processor (IOP) to execute the Serial ATA protocol. The term “specialized hardware” refers to dedicated hardware in a Serial ATA host controller, which is specifically designed to implement the Serial ATA protocol with minimum intervention from the IOP. The specialized hardware may give a performance advantage over implementing the Serial ATA protocol with the IOP and free up the IOP to perform other work. Generally, the IOP handles low-bandwidth transactions such as ATA PIO (Programmed Input/Output) transfers and then turns over control to the specialized hardware for higher-bandwidth transactions such as ATA DMA (Direct Memory Access) transfers.
There are three interface power states supported in Serial ATA: PhyReady, Partial and Slumber. In PhyReady (or power up) state, the PHY (physical) logic and main PLL (phase-locked loop) are both on and active, and the interface is synchronized and capable of receiving and sending data. Partial and Slumber are two power saving (or power down) modes. In both Partial and Slumber states, the PHY logic is powered, but is in a reduced power state. However, while the exit latency from Partial state is generally no longer than 10 μs (microseconds), the exit latency from Slumber state is generally no longer than 10 ms (milliseconds).
When a Serial ATA interface that utilizes a combination of IOP control and specialized hardware control is idle (ice., when either a Serial ATA host controller or an attached Serial ATA device is not active) for a period of time, it is desirable to put the interface into a power saving mode. In addition to saving power while in a power saving mode, the interface lifetime may be increased.
Thus, it would be desirable to provide a method and apparatus of automatic power management control which automatically puts a Serial ATA interface that utilizes a combination of IOP control and specialized hardware control into power up and power down modes.